Thanks to two recently released letters from his time in Taliban prison, Bowe Bergdahl has offered a bit of explanation as to why he left his base in June 2009. In the letters, addressed to his family and obtained by The Daily Beast, Bergdahl says that incompetent leadership and poor conditions led to his departure, and he implores those in charge of the investigation of his case to understand that there are "more sides" to the situation.
In the letter, dated March 23, 2013, he writes (words appear exactly as he wrote them):
"The cercomstance from the begaining of my time in Aphganistan from immedet top to bottum where bad for troopers espashly in my PLT. [...] Leadership was lacking, if not non-existent. The conditions were bad and looked to be getting worse for the men that where actuly the ones risking thier lives from the attack."
See the letter, and another dated November 2012, over at The Daily Beast.